The present invention relates to dual mode communication systems. More particularly, the present invention relates to a dual band radio frequency (RF) phone architecture which requires only a single transmit-receive switch.
Dual mode or dual band wireless telephones can operate in two different communication bands, such as, a global system for mobile (GSM) communication band or a digital communication service (DCS) communications band. The dual mode telephone or hand set typically includes a switch or control circuit for selecting operation in either the GSM band or DCS band.
The GSM band is between 890 and 960 megahertz (MHz), and the DCS band is between 1,710 and 1,880 MHz. A dual mode telephone operating in the GSM band transmits signals in the 890-915 MHz band and receives signals in the 935-960 MHz band. A dual mode telephone operating in the DCS band transmits signals in the 1,710-1,785 MHz band and receives signals in the 1,805-1,880 MHz band.
Conventional GSM/DCS dual mode phone architectures utilize separate transmit-receive switches for each band. With reference to FIG. 1, a conventional dual mode phone system 10 can include a GSM transmit circuit 12A, a DCS transmit circuit 12B, a GSM receive circuit 14A, a DCS receive circuit 14B, a GSM transmit-receive switch 16A, a DCS transmit-receive switch 16B, a diplexer 18, and an antenna 22. GSM transmit circuit 12A includes a GSM power amplifier 24A, and DCS transmit circuit 12B includes a DCS power amplifier 24B. GSM receive circuit 14A includes a mixer 32A and a GSM filter 34A, and DCS receive circuit 14B includes a DCS filter 34B and a mixer 32B.
In operation, system 10 receives and transmits GSM band signals on GSM path 40A and receives and transmits DCS signals on DCS path 40B. Paths 40A and 40B are in communication with antenna 22 via diplexer 18. Switches 16A and 16B receive transmit signals at an input 42 and provide the transmit signals to a diplexer interface 44. Switches 16A and 16B receive signals at diplexer interface 44 and provide the receive signals to a receive output 46.
Diplexer 18 also allows the simultaneous use of antenna 22 by both GSM and DCS switches 16A and 16B. Diplexer 18 separates GSM signals from DCS signals received from antenna 22 and provides the appropriate signals to paths 40A and 40B. Additionally, diplexer 18 isolates GSM signals on path 40A from DCS signals on path 40B and DCS signals on path 40B from GSM signals on path 40A.
Diplexer 18 can be a filter device having a low pass path coupled to path 40A and a high pass path coupled to path 40B. The high pass path and the low pass path preferably divide the frequency spectrum into two separate frequency bands, such as, the DCS band and the GSM band.
Transmit input 42 of switch 16A is coupled to power amplifier 24A in transmit circuit 12A. Similarly, transmit input 42 of switch 16B is coupled to power amplifier 24B of transmit circuit 12B. Receive output 46 of switch 16A is coupled to filter 34A in receive circuit 14A. Similarly, receive output 46 of switch 16B is coupled to filter 34B of receive circuit 14B. Switches 16A and B perform the basic function of routing the transmit and receive signals associated with paths 40A and B, respectively, to appropriate circuits 12A-B and 14A-B while providing adequate isolation. Switches 16A and B are preferably devices which do not have appreciable loss characteristics.
When in a transmit mode, switches 16A and B couple transmit input 42 to interface 44. When in a receive mode, switches 16A and B couple interface 44 to receive output 46. Switches 16A and B can be controlled by a control circuit or other device which places system 10 in a transmit or receive mode.
Transmit circuits 12A-B and receive circuits 14A-B preferably represent transmit and receive radio units for GSM and DCS bands in system 10. The various components associated with other portions of system 10 are beyond the scope of the general high level architecture associated with switches 16A and B and discussed in the present application.
System 10 is preferably implemented on a printed circuit board. The printed circuit board must be of minimal size in order to accommodate the decreasing size allowances for dual mode phones. Switches 16A and B consume a large portion (e.g., almost a majority) of the circuit board real estate associated with the circuit components shown in FIG. 1. Additionally, switches 16A and B and are expensive. Therefore, conventional switches 16A and B add significantly to the associated monetary and circuit board real estate costs of a dual mode phone design.
Thus, there is a need for a dual band phone architecture which only requires a single transmit-receive switch. Further, there is a need for a GSM/DCS dual mode phone architecture with reduced circuit board space requirements.
The present invention relates to a dual band phone including an antenna, a transmission path, a receive path, and a single transmit-receive switch. The transmission path includes a first transmit power amplifier and a second transmit power amplifier. The first transmit power amplifier provides transmit signals in a first frequency range, and the second transmit power amplifier provides the transmit signals in a second frequency range. The receive path includes a first filter path for receiving receive signals in a third frequency range and a second filter path for receiving receive signals in a fourth frequency range. The single transmit-receive switch has an antenna interface, a transmit input, and a receive output. The antenna interface is coupled to the antenna, the transmit input is coupled to the transmit path, and the receive output is coupled to the receive path.
The present invention further relates to a dual band phone architecture including a GSM radio transmission unit having a GSM output, a DCS radio transmission unit having a DCS output, at least one receive unit, a diplexer, and a single transmit-receive switch. The diplexer has a first input coupled to the GSM output, a second input coupled to the DCS output, and a diplexer output. The single transmit-receive switch has an antenna interface, a transmit input, and a receive output. The transmit input is coupled to the diplexer output, and the receive output is coupled to the receive unit.
The present invention still further relates to a dual band phone system including an antenna, a transmission path means, a receive path means, and a single transmit-receive switch means. The transmission path means provides transmit signals in a first frequency range and in a second frequency range. The receive path means receives receive signals in a third frequency range and in a fourth frequency range. The single transmit-receive switch means connects the transmission means to an antenna or the receive path means to the antenna.
According to one exemplary aspect of the present invention, a phone architecture utilizes only a single transmit-receive switch. A GSM-DCS diplexer is used to separate GSM and DCS signal paths before the transmit-receive switch. A low pass filter can be used to suppress harmonics in the individual GSM and DCS paths. The transmit-receive switch is preferably broad band enough to cover both GSM and DCS frequency bands and is disposed just before the antenna.
In accordance with another exemplary aspect of the present invention, the GSM and DCS power amplifiers can be switched off, depending upon the mode of operation (GSM mode or DCS mode). The transmit-receive switch preferably operates across the frequency range of 890 to 1880 MHz at a power of 35 dbm at GSM frequency bands and 32 dbm at DCS frequency bands. The transmit-receive switch is a GaAs device having low insertion losses between 0.5 dB to 1 dB in both DCS and GSM bands. In addition to simplifying conductor routing for the dual mode phone, the use of a single switch reduces requirements for both circuit board space and electrical current.